Float valve controlled tote - Kratky method

I set up a float valve controlled 27-gallon tote for Kratky method growing. I'll post updates on how it does over the course of the season.
 

https://youtu.be/fgr1XYrZsy8

Very nice DIY video. 

indeed, thanks for this highly informative video- you make it seem too easy! Now I'm tempted to try this next season too and will have to scavenge for parts this coming winter...

Hi Peter, I just re-watched this video as I have a bunch of starts in hydro that I want to keep in hydro and think this may be a good way to have multiple plants fed from a single reservoir. I'm likely going to have large 32gallon bin as a master reservoir and an intermediate bucket with the float valve in it then feeding on to 6 or more 5-gallon buckets with the plants in. I'm going to use the 6" net put bucket lids.
 
My question for you is what nutrient level to keep? I'm thinking that initially the plants may not have much in the way of roots below the 6" net pot so I'd want to keep the level close to the net pot but as they grow, the level can go down but what would the minimum level be? 6" or more?